This invention relates to apparatus and a method for enhancing the playback fidelity of digital disks. Such disks, also called "laser disks", "compact disks" or simply "CD's", are widely used for musical recording as well as video and information storage and retrieval.
A CD typically consists of a recording medium of transparent plastic, associated with a layer of protective material. Data, which in the case of audio recording constitutes an acoustic waveform expressed in digital (binary) code, is placed on the recording medium as a series of microscopic "pits" of differing lengths and constant depth. The pits are arranged in a spiral track around the center of the disk. A reflective coating is applied to the pitted surface, and the protective layer is applied over that. The pits are typically between about 1 and 3 micrometers in length and about 0.5 micrometers wide. In playback, a laser beam is focused on the pit track from beneath the rapidly spinning disk, and "reads" the pits and the spaces between them, by sensed reflection, as a stream of "zeros" and "ones". The track is scanned at a constant linear rate of about four feet/second, a rate which translates into rotation when sensing is at the center at about 500 revolutions per minute, slowing to about 200 revolutions per minute as scanning reaches the outer periphery of the disk.